1. Field of the Invention
The present invention relates to an intermediate transfer unit for the secondary transfer onto sheet of developed images that were primarily transferred onto a plurality of image carriers, and an image forming apparatus comprising the intermediate transfer unit.
2. Description of the Related Art
In a conventional image forming apparatus having an intermediate transfer unit between a toner container for containing developer (toner) and a developing device, a toner supply pipe for supplying toner from the toner container to the developing device is provided such that the pipe detours around a housing of the intermediate transfer unit. Such an arrangement is disclosed in, for example, FIG. 7 of Japanese Unexamined Patent Publication No. 2004-139031.
FIG. 40 of this specification is a citation of FIG. 7 from the above patent document. As shown in FIG. 40, a setting space S between a toner container 32Y and a developing device 6Y is a space for setting the intermediate transfer unit (not shown). With this arrangement, a toner supply pipe 43Y for supplying toner from the toner container 32Y to the developing device 6Y is provided such that it detours and thus curves around the setting space S for the intermediate transfer unit. Since the toner supply pipe 43Y curves, a conveying member (not shown) such as a screw for conveying toner is provided inside the toner supply pipe 43Y.
However, the arrangement in the above patent document needs to provide a toner supply port of the toner container 32Y outside the developing device 6Y, which necessitates such a design that the toner container 32Y has a width larger than that of the developing device 6Y. This results in preventing size reduction of the image forming apparatus. An arrangement is also considered that the toner container 32Y is designed to have the same width as the developing device 6Y. However, the toner supply pipe 43Y must be provided such that it detours around the setting space S for the intermediate transfer unit even in such a case. Therefore, the image forming apparatus thus must be enlarged in its width direction according to that of the toner supply pipe 43Y, resulting in an image forming apparatus that cannot be made smaller. Further, when the toner supply pipe 43Y curves, there arises a necessity to provide the conveying member inside the toner supply pipe 43Y, which also limits down-sizing of the image forming apparatus since the toner supply pipe 43Y becomes larger.
In a color image forming apparatus comprising a plurality of sets of toner containers and developing devices, the task of connecting these toner containers and developing devices respectively to each other through toner supply pipes becomes necessary when manufacturing and maintaining the apparatus, which results in low productivity and inconvenient maintenance.